Disconnect one of the battery cables, and see if you get a spark when you touch the cable back to the battery post. If so, there's a constant drain that's responsible for the battery failing. If not, the alternator might not be charging. Check the voltage at the battery with the engine stopped. It should be about 12.5 volts with a well-charged battery. Running voltage at the battery, also with a full-charged battery, should be between 13.5 and 14.5 volts. When the alternator is recharging a low battery, the voltage might drop as low as 13, but the charging current will be high, 60 amps or more. As the battery recharges, the amp rate will drop, and the voltage will increase. A good-condition, well-charged battery should drop the amp rate to 10 or less, and the voltage should go well above 14 volts. Do you have an internally-regulated alternator, or is there a voltage regulator somewhere in the circuit? The wiring will be very different, depending on what type of alternator you've got.
Jerry
